Quote from Lojanica:
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A dual cpu motherboard with at least 2x pcie x 16 slots will give you flexibility to adapt as hardware ages. If you buy a mid-range CPU and video card now but have a good motherboard with ample power you can build an affordable system with good capabilities but have the option to add as needed. The bonus with mid-range video and CPU's in a dual socket motherboard is that as time goes by those components will drop like a rock in price but all you have to do is double up and you just doubled your capabilities without having to nuke your system or invest a lot. You can generally skip one cycle of upgrading at the same price as mid- high range gear.
How good is a dual CPU motherboard when Intel came up with their Sandy Bridge chips (marketed as "second generation" i3 i5 i7)... basically pretty much boosted the speed by >50% of their predecessors and selling for about the same price (around $300)? In just one year's time...
i7-930 2.80GHz still sells for $240. (I bought mine a year ago for about $280).